Carbon–Mercury Interactions in Spodosols Assessed through Density Fractionation, Radiocarbon Analysis, and Soil Survey Information
Bibliographic record
Abstract
Core Ideas Bulk soils are mixtures of SOM pools that cycle C and Hg very differently. Density separation and C‐14 analysis reveal differences between SOM pools. Mineral interactions are an underappreciated mechanism for Hg and C stabilization. C‐Hg interactions in Spodosols are consistent across the entire soil order. Soil taxonomic orders differ in C‐Hg relationships in pedogenically predictable ways. Soils comprise the largest terrestrial pool of C and Hg on Earth, and these elements have critical feedbacks to problems ranging from atmospheric pollution and climate change to public health. Empirical evidence suggests these elements cycle closely in a wide range of soils, but mechanistic studies of their interactions within distinct soil organic matter (SOM) pools and between different soil types are needed. Here, we report findings of a novel approach to investigate C–Hg interactions, primarily in Spodosols, in which we: (i) examined density separated topsoil and illuvial horizons of four contrasting Spodosols, and used radiocarbon to investigate interactions between Hg and C cycling in distinct SOM pools; (ii) assessed broader patterns across Spodosols and other soil orders using USDA soil survey laboratory data. Consistent with other studies, C and Hg concentrations of individual soil horizons were positively related across the four contrasting Spodosols. Carbon and Hg were also positively related in the density fractions comprising individual soil horizons, but radiocarbon analysis revealed fundamental differences in Hg retention in modern, C‐rich fractions vs. low‐C fractions containing less modern radiocarbon. The lack of significant site‐to‐site variation in C and Hg across these sites (and Spodosols more broadly), contrasted against significant differences between horizons and fractions, suggests processes controlling C–Hg interactions are consistent across the taxonomic order. Furthermore, significant differences between other soil orders indicate that processes controlling soil formation—as represented by soil taxonomy—can explain differences in C–Hg interactions and their distribution across soils.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".